Liquid Crystal Display Device

ABSTRACT

A liquid crystal display device in which a liquid crystal layer is sandwiched between a TFT substrate having pixel electrodes and opposed electrodes formed and an opposed substrate, an external conductive film of a transparent electrode is formed on an outer surface of the opposed substrate, and an upper polarizing plate is arranged on the external conductive film. A portion of the external conductive film that is not covered with the upper polarizing plate is electrically connected to a ground potential through a conductive thermocompression bonding tape. The conductive thermocompression bonding tape is configured so that w 3&lt; w 2&lt; w 1  is satisfied, wherein w 1  represents a width of the conductive thermocompression bonding tape, w 2  represents the width of the conductive thermocompression bonding tape electrically connected to the external conductive film, and w 3  represents the width of the conductive thermocompression bonding tape electrically connected to a predetermined portion where the ground potential is provided.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/558,411, filed Jul. 26, 2012, the contents of which are incorporatedherein by reference.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2011-167303 filed on Jul. 29, 2011, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andparticularly to a grounding method of a shield conductive film formed onan opposed substrate in an IPS-type liquid crystal display device.

2. Description of the Related Art

In a liquid crystal display device, there are provided a TFT substrateon which pixel electrodes, thin-film transistors (TFTs) and the like arearranged in matrix, and an opposed substrate which faces the TFTsubstrate and on which color filters and the like are formed atpositions corresponding to the pixel electrodes of the TFT substrate. Inaddition, liquid crystal is sandwiched between the TFT substrate and theopposed substrate. Further, the transmission of light of liquid crystalmolecules is controlled for each pixel to form an image.

Since a liquid crystal display device is flat and lightweight, it hasbeen widely used in various fields ranging from large-sized displaydevices such as TVs to cellular phones and DSCs (Digital Still Cameras).On the other hand, the characteristic of viewing angles is important ina liquid crystal display device. The characteristic of viewing angles isa phenomenon in which the brightness and chromaticity are changed whenviewing the screen from a front or oblique direction. The characteristicof viewing angles is excellent in an IPS (In Plane Switching) type inwhich liquid crystal molecules are operated by an electric field in thehorizontal direction.

In the IPS type, both of pixel electrodes and opposed electrodes areformed on the TFT substrate, and no electrodes are formed inside theopposed substrates. In such a structure, an electric field from outsideenters a liquid crystal layer to become noise, deteriorating the imagequality.

In order to prevent this problem, Japanese Patent Application Laid-OpenNo. Hei 9-105918 describes a configuration in which an externalconductive film is formed outside an opposed substrate by sputtering ITO(Indium Tin Oxide) and the like and then is grounded, so that the insideof the liquid crystal display device is shielded. As grounding methodsof the external conductive film, Japanese Patent Application Laid-OpenNo. Hei 9-105918 describes a method in which the external conductivefilm is connected to a metal frame through a conductive material and amethod in which the external conductive film is connected to an earthterminal of a surrounding substrate through a cable. U.S. Pat. No.6,034,757 exists as the corresponding patent of Japanese PatentApplication Laid-Open No. Hei 9-105918.

In the method in which the external conductive film is directlyconnected to a metal frame through a conductive material, the externalconductive film and a relatively-large connection area are required inconsideration of accuracy of embedding the liquid crystal display deviceinto a frame. However, a polarizing plate is arranged on the opposedsubstrate, and thus it is difficult to sufficiently provide an areawhere the external conductive film is connected to an outside earthterminal. In recent years, it has been required to increase a displayarea while keeping the outer shape of the liquid crystal display deviceat a predetermined value. In addition, a portion of the externalconductive film that is not covered with the polarizing plate, namely,the exposed area of the external conductive film has been furtherdecreased.

On the other hand, in the method in which the external conductive filmof the opposed substrate is connected to an earth terminal of a wiringsubstrate or the like through a cable, it is difficult to secure thereliability of connection between the cable and the external conductivefilm of the opposed substrate.

An object of the present invention is to ground an external conductivefilm formed on an opposed substrate with a high degree of reliability inan IPS-type liquid crystal display device.

SUMMARY OF THE INVENTION

The present invention solves the above-described problem, and mainfeatures are as follows. Specifically, there is provided a liquidcrystal display device in which a liquid crystal layer is sandwichedbetween a TFT substrate having pixel electrodes and opposed electrodesformed and an opposed substrate having color filters formed, an externalconductive film of a transparent electrode is formed on an outer surfaceof the opposed substrate, and an upper polarizing plate is arranged onthe external conductive film, wherein an earth pad connected to theground is formed on the TFT substrate, a portion of the externalconductive film that is not covered with the upper polarizing plate isconnected to the earth pad through a conductive thermocompressionbonding tape, and w3<w2<w1 is satisfied, if a direction parallel with aside of the opposed substrate on which the conductive thermocompressionbonding tape is arranged is defined as a width, where w1 represents thewidth of the conductive thermocompression bonding tape, w2 representsthe width of the conductive thermocompression bonding tape adhering tothe external conductive film, and w3 represents the width of theconductive thermocompression bonding tape adhering to the earth pad.

More preferably, 1.2w3≦w2≦2.4w3<w1 is satisfied in the liquid crystaldisplay device where w1 represents the width of the conductivethermocompression bonding tape, w2 represents the width of theconductive thermocompression bonding tape adhering to the externalconductive film, and w3 represents the width of the conductivethermocompression bonding tape adhering to the earth pad.

According to the present invention, it is possible to ground an externalconductive film formed on an opposed substrate with a high degree ofreliability in an IPS-type liquid crystal display device. Thus, it ispossible to realize a highly reliable IPS-type liquid crystal displaydevice that is excellent in the image quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a liquid crystal display device to which thepresent invention is applied;

FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1;

FIG. 3 is a plan view for showing the present invention;

FIG. 4 is a cross-sectional view for showing connection using aconductive thermocompression bonding tape;

FIGS. 5A and 5B show a thermocompression bonding head used in thepresent invention;

FIGS. 6A and 6B are diagrams each showing the shape of the conductivethermocompression bonding tape;

FIG. 7 is a plan view for showing another mode of the present invention;

FIG. 8 is a plan view for showing a first comparison example;

FIGS. 9A and 9B show a thermocompression bonding head used in the firstcomparison example;

FIG. 10 is a plan view for showing a second comparison example;

FIGS. 11A and 11B show a thermocompression bonding head used in thesecond comparison example;

FIG. 12 is a plan view for showing a third comparison example;

FIGS. 13A and 13B show a thermocompression bonding head used in thethird comparison example;

FIG. 14 is a plan view for showing another mode of the third comparisonexample; and

FIG. 15 is a cross-sectional view of a display area of an IPS liquidcrystal display device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Before explaining an embodiment of the present invention, a structure ofan IPS-type liquid crystal display device to which the present inventionis applied will be described. FIG. 15 is a cross-sectional view forshowing a structure in a display area of an IPS-type liquid crystaldisplay device. For the IPS-type liquid crystal display device, variouselectrode structures have been proposed and put to practical use. Thestructure shown in FIG. 15 is being widely used today. In simple terms,a comb-like pixel electrode 110 is formed on a planar opposed electrode108 while sandwiching an insulating film. Liquid crystal molecules 301are rotated with voltage between the pixel electrode 110 and the opposedelectrode 108, so that the transmission of light of a liquid crystallayer 300 is controlled for each pixel to form an image. Hereinafter,the structure shown in FIG. 15 will be described in detail. It should benoted that the present invention will be described using theconfiguration shown in FIG. 15 as an example. However, the presentinvention can be applied to an IPS-type liquid crystal display deviceother than that shown in FIG. 15.

In FIG. 15, a gate electrode 101 is formed on a TFT substrate 100 madeof glass. The gate electrode 101 is covered with a gate insulating film102 made of SiN. A semiconductor layer 103 of an a-Si film is formed onthe gate insulating film 102 at the position opposed to the gateelectrode 101. The a-Si film forms a channel part of the TFT, and asource electrode 104 and a drain electrode 105 are formed on the a-Sifilm while sandwiching the channel part. It should be noted that an n+Silayer (not shown) is formed between the a-Si film and the sourceelectrode 104 or the drain electrode 105. The n+Si layer is formed toprovide an ohmic contact between the semiconductor layer and the sourceelectrode 104 or the drain electrode 105.

The source electrode 104 is also used by a video signal line, and thedrain electrode 105 is connected to the pixel electrode 110. Both of thesource electrode 104 and the drain electrode 105 are simultaneouslyformed on the same layer. The TFT is covered with an inorganicpassivation film 106 made of SiN. The inorganic passivation film 106protects especially the channel part of the TFT from impurities 401. Onthe inorganic passivation film 106, formed is an organic passivationfilm 107. The organic passivation film 107 functions to flatten thesurface as well as to protect the TFT, and thus the thickness thereof islargely formed. The thickness thereof ranges from 1 μm to 4 μm.

The opposed electrode 108 is formed on the organic passivation film 107.The opposed electrode 108 is formed by sputtering ITO (Indium Tin Oxide)of a transparent conductive film on the entire display area.Specifically, the opposed electrode 108 is formed in a planar shape. Theopposed electrode 108 is formed on the entire surface by sputtering, andthen only a through-hole 111 conducting the pixel electrode 110 and thedrain electrode 105 to each other is formed by etching the opposedelectrode 108.

The opposed electrode 108 is covered with an upper insulating film 109made of SiN. Following the formation of the upper insulating film 109,the through-hole 111 is formed by etching. The through-hole 111 isformed by etching the inorganic passivation film 106 while using theupper insulating film 109 as a resist. Thereafter, ITO serving as thepixel electrode 110 is formed by sputtering while covering the upperinsulating film 109 and the through-hole 111. The sputtered ITO ispatterned to form the pixel electrode 110.

In FIG. 15, the pixel electrode 110 is formed in a comb-like shape, anda slit 112 is formed between the comb-like electrodes as shown in FIG.15. Constant voltage is applied to the opposed electrode 108, and thevoltage of a video signal is applied to the pixel electrode 110. Whenvoltage is applied to the pixel electrode 110, lines of electric forceare generated as shown in FIG. 15 to rotate the liquid crystal molecules301 in the line direction of electric force, so that the transmission oflight from a backlight is controlled. Since the transmission from thebacklight is controlled for each pixel, an image is formed. On the pixelelectrode 110, formed is an alignment film 113.

In FIG. 15, an opposed substrate 200 is provided while sandwiching theliquid crystal layer 300. Color filters 201 are formed inside theopposed substrate 200. Red, green, and blue color filters 201 are formedfor each pixel to form a color image. A black matrix 202 is formedbetween the color filters 201 to improve the contrast of an image. Thecolor filters 201 and the black matrix 202 are covered with an overcoatfilm 203. On the overcoat film 203, formed is the alignment film 113 toset the initial alignment of liquid crystal. A photo-alignment processis performed for the alignment film 113.

As described above, the pixel electrode 110 and the opposed electrode108 are formed on the TFT substrate 100 in the IPS liquid crystaldisplay device, and no electrodes are formed inside the opposedsubstrate 200. Thus, an electric field enters the liquid crystal layer300 or the pixel electrode 110 from outside in this state to generatenoise, thus deteriorating the image quality.

In order to prevent this problem, an external conductive film 210 usinga transparent conductive film such as ITO is formed outside the opposedsubstrate 200 in the IPS-type liquid crystal display device, and theexternal conductive film 210 is grounded to shield the inside of theliquid crystal display device. However, a large part of the surface ofthe opposed substrate 200 is covered with an upper polarizing plate 70as will be described later, and the exposed area of the externalconductive film 210 is small. Accordingly, it is an important issue toground the external conductive film 210 with a high degree ofreliability.

First Embodiment

FIG. 1 is a plan view of a liquid crystal display device to which thepresent invention is applied and which is used for, for example,cellular phones. In FIG. 1, an opposed substrate 200 adheres onto a TFTsubstrate 100 through a seal member (not shown). The TFT substrate 100is formed larger in size than the opposed substrate 200, and the area ofonly the TFT substrate 100 serves as a terminal part 150.

An external conductive film 210 made of ITO is formed outside theopposed substrate 200. On the ITO, attached is an upper polarizing plate70. As shown in FIG. 1, the upper polarizing plate 70 covers a largepart of the opposed substrate 200, and the external conductive film 210is slightly exposed at peripheral areas. The peripheral small areas needto be grounded by being connected to an earth pad 20 formed on the TFTsubstrate 100-side.

In the present invention, the external conductive film 210 exposedaround the opposed substrate is connected to the earth pad 20 formed onthe TFT substrate 100 using a conductive thermocompression bonding tape10. The earth pad 20 is connected to an earth terminal of a flexiblewiring substrate 50 connected to the terminal part 150 or an earthterminal of an IC driver 40 formed at the terminal part 150 through anearth line 21.

FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1. InFIG. 2, a liquid crystal layer (not shown) is sandwiched between the TFTsubstrate 100 and the opposed substrate 200. A lower polarizing plate 60adheres to the lower side of the TFT substrate 100. The externalconductive film 210 made of ITO is formed on the upper side of theopposed substrate 200. The upper polarizing plate 70 is attached on theexternal conductive film 210.

In order to shield the inside of the liquid crystal display device, itis necessary to ground the external conductive film 210. Since the earthpad 20 is formed on the TFT substrate 100, the external conductive film210 of the opposed substrate 200 is connected to the earth pad 20 of theTFT substrate 100 using the conductive thermocompression bonding tape10. As shown in FIG. 2, a step having the thickness of the TFT substrate100 is provided between the external conductive film 210 of the opposedsubstrate 200 and the earth pad 20 of the TFT substrate 100. In order torealize the connection in this state, the conductive thermocompressionbonding tape 10 is connected to the external conductive film 210 of theopposed substrate 200 and the earth pad 20 of the TFT substrate 100using a thermocompression bonding head 30 having a step at its tip endas shown in FIG. 4.

There is a problem in this connection configuration that the width d1 ofa portion of the external conductive film 210 of the opposed substrate200 that is not covered with the upper polarizing plate 70 is as smallas about 0.9 mm. Further, the conductive thermocompression bonding tape10 is connected at temperatures of 120° C. to 140° C. with thethermocompression bonding head 30. If the thermocompression bonding head30 is brought into contact with the upper polarizing plate 70, an endportion of the upper polarizing plate 70 is broken. Thus, it isnecessary to secure an interval d2 of a predetermined value, forexample, about 0.4 mm between the upper polarizing plate 70 and theconductive thermocompression bonding tape 10. The value 0.4 mm is avalue obtained in consideration of the margin of work.

In such a configuration, the width at which the conductivethermocompression bonding tape 10 can be connected to the externalconductive film 210 of the opposed substrate 200 is about 0.5 mm. Thus,the reliability of connection between the external conductive film 210of the opposed substrate 200 and the conductive thermocompressionbonding tape 10 becomes particularly important.

In the present invention, the conductive area and the contact area ofthe conductive thermocompression bonding tape 10 on the opposedsubstrate 200 are increased using the thermocompression bonding head 30as shown in FIGS. 5A and 5B. FIG. 5A is a cross-sectional view of thethermocompression bonding head 30 and FIG. 5B is a bottom view of thethermocompression bonding head 30. In FIG. 5B, the width w2 of a portionconnecting to the external conductive film 210 of the opposed substrate200 is larger than the width w3 of a portion connecting to the earth pad20 of the TFT substrate 100. The contact area on the external conductivefilm 210 can be increased by this amount.

FIG. 3 is a plan view for showing a portion to which the conductivethermocompression bonding tape 10 is connected in such a manner. In FIG.3, the conductive thermocompression bonding tape 10 connects theexternal conductive film 210 of the opposed substrate 200 to the earthpad 20 of the TFT substrate 100. The conductive thermocompressionbonding tape 10 of FIG. 3 is formed in a square shape, and widths w1 andw4 are, for example, 3 mm. It is obvious that the widths w1 and w4 aredifferent from each other in some cases. Electric conduction and contactare realized not through the entire conductive thermocompression bondingtape but only a part of the conductive thermocompression bonding tapebonded by thermocompression of the thermocompression bonding head 30.Specifically, electric conduction is realized by a conductive area 15 ofFIG. 3.

As shown in FIG. 3, the contact and electric conduction of theconductive thermocompression bonding tape 10 is as wide as a width w2 onthe external conductive film 210 of the opposed substrate 200 and is asnarrow as a width w3 on the earth pad 20 of the TFT substrate 100. Inthe embodiment, the width w2 is 2 mm and the width w3 is 1 mm. In orderto increase adhesive force on the opposed substrate 200, the width w2needs to be at least 1.2 times the width w3. More preferably, the widthw2 needs to be at least twice the width w3.

On the other hand, it is necessary to provide a distance g of at least0.3 mm from the contact portion or the conductive portion to an end ofthe conductive thermocompression bonding tape 10. This is because theaccuracy of thermocompression work by the thermocompression bonding head30 is about ±0.2 mm, and it is necessary to provide the distance g of atleast 0.1 mm between the an end of thermocompression bonding head 30 andan end of the conductive thermocompression bonding tape 10. When thewidth w1 is 3 mm and the distance g is 0.3 mm, the width w2 is 2.4 mm.In this case, the width w3 is 1 mm, and thus the width w2 is 2.4 timesthe width w3.

In FIG. 3, the conductive thermocompression bonding tape 10 is connectedto the earth pad 20 on the TFT substrate 100, and the earth pad 20 isconnected to the flexible wiring substrate 50 and the like through theearth line 21. Further, the exposed width d1 of the external conductivefilm 210 of the opposed substrate 200 is 0.9 mm and a distance d2between an end of the conductive thermocompression bonding tape 10 andan end of the upper polarizing plate 70 is 0.4 mm in FIG. 3.

FIGS. 6A and 6B are detailed diagrams each showing an example of theconductive thermocompression bonding tape 10. The conductivethermocompression bonding tape 10 of FIGS. 6A and 6B is largely dividedinto three parts in the cross-section, specifically, an adhesive tape 11with a small adhesive force (for example, a thickness of 85 μm), aconductive adhesive sheet 12 (for example, a thickness of 45 μm), and atwo-sided adhesive tape 13 (for example, a thickness of 30 μm) in orderfrom the top. Of these layers, it is the conductive adhesive sheet 12that exhibits the adhesiveness and conductivity by thermocompression.

The two-sided adhesive tape 13 of FIGS. 6A and 6B is used to temporarilyattach the conductive thermocompression bonding tape 10 to the TFTsubstrate 100 or the opposed substrate 200 before thermocompression ofthe conductive thermocompression bonding tape 10. In FIGS. 6A and 6B,the two-sided adhesive tape 13 is formed across a width w5, and w5/w1 is⅓ in FIGS. 6A and 6B.

When the thermocompression bonding head 30 abuts on the area where thetwo-sided adhesive tape 13 is formed, the two-sided adhesive tape 13 iscrashed and protrudes outside. FIG. 7 shows a state in which an area 16where the two-sided adhesive tape 13 protrudes exists when thethermocompression bonding head 30 of the present invention is used. Ifthe two-sided adhesive tape 13 protrudes, the two-sided adhesive tape 13adheres to the thermocompression bonding head 30, deteriorating theefficiency of the following work or the adhesive accuracy in some cases.In the connection method of the present invention, the amount ofprotrusion of the two-sided adhesive tape 13 is extremely small as shownin FIG. 7, and thus the deterioration in the work efficiency andadhesive accuracy can be suppressed to a small degree.

FIRST COMPARISON EXAMPLE

FIGS. 8, 9A and 9B show a first comparison example relative to thepresent invention. FIG. 8 is an enlarged view of a portion where theconductive thermocompression bonding tape 10 is arranged in the liquidcrystal display device, and corresponds to FIG. 3 of the firstembodiment. FIG. 8 is different from FIG. 3 in that the width of aportion of the conductive thermocompression bonding tape 10 adhering orconducting to the external conductive film 210 of the opposed substrate200 is equal to the width w1 of the conductive thermocompression bondingtape 10.

Each of FIGS. 9A and 9B shows the shape of the thermocompression bondinghead 30 to connect the conductive thermocompression bonding tape 10shown in FIG. 8. FIG. 9A is a cross-sectional view thereof, and FIG. 9Bis a bottom view thereof. FIGS. 9A and 9B are different from thethermocompression bonding head 30 used in the embodiment in that thewidth of the head 30 attached to the opposed substrate 200-side is equalto the width w1 of the conductive thermocompression bonding tape 10.

If the width of a portion of the conductive thermocompression bondingtape 10 adhering to the external conductive film 210 is large, thereliability of adhesion between the opposed substrate 200 and theconductive thermocompression bonding tape 10 is enhanced. However, theamount of protrusion of the two-sided adhesive tape 13 becomes large,thus increasing the possibility that the adhesive material adheres tothe thermocompression bonding head 30. As a result, the workability ofthermocompression or the work accuracy of thermocompression isdeteriorated.

SECOND COMPARISON EXAMPLE

FIGS. 10, 11A and 11B show a second comparison example relative to thepresent invention. FIG. 10 is an enlarged view of a portion where theconductive thermocompression bonding tape 10 is arranged in the liquidcrystal display device, and corresponds to FIG. 3 of the firstembodiment. FIG. 10 is different from FIG. 3 in that thethermocompression bonding head 30 is attached to the entire conductivethermocompression bonding tape 10 by thermocompression, and theconductive thermocompression bonding tape 10 is connected to theexternal conductive film 210 of the opposed substrate 200 and the earthpad 20 of the TFT substrate 100.

Each of FIGS. 11A and 11B shows the shape of the thermocompressionbonding head 30 to connect the conductive thermocompression bonding tape10 shown in FIG. 10. FIG. 11A is a cross-sectional view thereof, andFIG. 11B is a bottom view thereof. In FIG. 11 B, the outer shape of thelower surface of the thermocompression bonding head 30 is the same asthat of the conductive thermocompression bonding tape 10.

Since the entire conductive thermocompression bonding tape 10 adheres tothe external conductive film 210 of the opposed substrate 200 or theearth pad 20 of the TFT substrate 100 in FIG. 10, the reliability ofadhesiveness or conduction is enhanced. However, the two-sided adhesivetape 13 largely protrudes from the conductive thermocompression bondingtape 10 as shown in FIG. 10. As a result, the adhesive material 13adheres to the thermocompression bonding head 30, deteriorating theworkability of thermocompression or the work accuracy ofthermocompression.

THIRD COMPARISON EXAMPLE

FIGS. 12, 13A, 13B and 14 show a third comparison example relative tothe present invention. FIG. 12 is an enlarged view of a portion wherethe conductive thermocompression bonding tape 10 is arranged in theliquid crystal display device, and corresponds to FIG. 3 of the firstembodiment. FIG. 12 is different from FIG. 3 in that the conductivethermocompression bonding tape 10 is connected to the externalconductive film 210 of the opposed substrate 200 and the earth pad 20 ofthe TFT substrate 100 through a constant width w3 in the middle.

Each of FIGS. 13A and 13B shows the shape of the thermocompressionbonding head 30 to connect the conductive thermocompression bonding tape10 shown in FIG. 12. FIG. 13A is a cross-sectional view thereof, andFIG. 13B is a bottom view thereof. In FIG. 13B, the outer shape of thelower surface of the thermocompression bonding head 30 is not a T shapebut a rectangular shape with a width w1. In the comparison example, thewidth is, for example, 1 mm.

In FIG. 12, the conductive thermocompression bonding tape 10 isconnected to the external conductive film 210 of the opposed substrate200 only through the width w1. Thus, it is impossible to sufficientlysecure the reliability of adhesive strength and conduction to theexternal conductive film 210 of the opposed substrate 200. FIG. 14 showsa state of the two-sided adhesive tape 13 in the conductivethermocompression bonding tape 10 in the third comparison example. Inthe comparison example, the area of the two-sided adhesive tape 13 ofthe conductive thermocompression bonding tape 10 is not bonded bythermocompression if the variation of work is not considered. Thus, itis less likely that the two-sided adhesive tape 13 adheres to thethermocompression bonding head 30 to deteriorate the workability ofthermocompression or the accuracy of the thermocompression dimension.

What is claimed is:
 1. A liquid crystal display device in which a liquidcrystal layer is sandwiched between a TFT substrate having pixelelectrodes and opposed electrodes formed and an opposed substrate, anexternal conductive film of a transparent electrode is formed on anouter surface of the opposed substrate, and an upper polarizing plate isarranged on the external conductive film, wherein a portion of theexternal conductive film that is not covered with the upper polarizingplate is electrically connected to a ground potential through aconductive thermocompression bonding tape, and wherein the conductivethermocompression bonding tape is configured so that w3<w2<w1 issatisfied, if a direction parallel with a side of the opposed substrateon which the conductive thermocompression bonding tape is arranged isdefined as a width, where w1 represents the width of the conductivethermocompression bonding tape, w2 represents the width of theconductive thermocompression bonding tape electrically connected to theexternal conductive film, and w3 represents the width of the conductivethermocompression bonding tape electrically connected to a predeterminedportion where the ground potential is provided to the predeterminedportion.
 2. The liquid crystal display device according to claim 1,wherein 1.2w3≦w2≦2.4w3<w1 is satisfied, and wherein the opposedsubstrate has color filters formed thereon.
 3. The liquid crystaldisplay device according to claim 2, wherein a two-sided adhesive tapefor temporary bonding is formed at a part of the conductivethermocompression bonding tape.
 4. The liquid crystal display deviceaccording to claim 3, wherein the liquid crystal display device is anIPS type liquid crystal display device.
 5. The liquid crystal displaydevice according to claim 1, wherein an earth pad electrically connectedto the ground potential is formed on the TFT substrate, and wherein theportion of the external conductive film that is not covered with theupper polarizing plate is connected to the earth pad through theconductive thermocompression bonding tape.
 6. A liquid crystal displaydevice in which a liquid crystal layer is sandwiched between a TFTsubstrate having pixel electrodes and opposed electrodes formed and anopposed substrate, an external conducive film of a transparent electrodeis formed on an outer surface of the opposed substrate, and an upperpolarizing plate is arranged on the external conductive film, wherein aportion of the external conductive film that is not covered with theupper polarizing plate is electrically connected to a fixed potentialthrough a conductive thermocompression bonding tape, and whereinw3<w2<w1 is satisfied, if a direction parallel with a side of theopposed substrate on which the conductive thermocompression bonding tapeis arranged is defined as a width, where w1 represents the width of theconductive thermocompression bonding tape, w2 represents the width ofthe conductive thermocompression boding tape electrically connected tothe external conductive film, and w3 represents the width of theconductive thermocompression bonding tape electrically connected to apredetermined portion, wherein the fixed potential is provided to thepredetermined portion.
 7. The liquid crystal display device according toclaim 6, wherein an earth pad electrically connected to the fixedpotential is formed on the TFT substrate, wherein the portion of theexternal conductive film that is not covered with the upper polarizingplate is connected to the earth pad through the conductivethermocompression bonding tape, and wherein the opposed substrate hascolor filters formed thereon.